Japanese Patent Application Publication No. 2011-090443 discloses a projection type capacitance touch panel in which a column electrode extending in a first direction and a row electrode extending in a second direction intersecting the first direction are formed on one surface of a single base.
The touch panel disclosed in Japanese Patent Application Publication No. 2011-090443 may be used as a flat panel or may be molded in a predetermined three-dimensional shape depending on the purpose. For example, a touch panel having a hemispherical shape obtained by molding a flat film sensor may be installed in a driver seat of a vehicle, and the touch panel may be used for a driver's manipulation using finger touch.
A touch panel having such a hemispherical shape or another three-dimensional shape is generally molded by thermoforming. When the thermoforming is performed, materials need to be stretched. Therefore, a base film is made of, e.g., PET film/sheet and PC film/sheet. Further, an electrode is made of a metal that is stretched during thermoforming (e.g., copper or indium); powdered silver mixed with a resin binder; PEDOT (polyethylene dioxythiophene) or the like.
In vacuum forming, which is one of the thermoforming methods, a film sensor is disposed above a mold in a vacuum chamber with an electrode facing up. The film sensor is heated by infrared rays from the electrode side while maintaining the vacuum chamber in a vacuum state, and the film sensor is stretched by pressing the mold disposed below the film sensor toward the film sensor. Therefore, the film sensor is formed in a three-dimensional shape.
Further, in a case when a decorative film is attached to the film sensor thus formed, an OCA (Optical Clear Adhesive) is provided as an adhesive agent on a bottom surface of a decorative film having a predetermined pattern, and the decorative film is laminated on the three-dimensionally formed film sensor. The decorative film is adhered to the film sensor by performing the vacuum forming again. Accordingly, an integrally molded touch panel is obtained.
In the thermoforming method such as vacuum forming, the film sensor is made of a stretchable material in consideration of stretching in the forming (molding) process and the electrode is made of, e.g., a mixture of powdered silver having conductivity and a thermoplastic resin binder.
In that case, as shown in FIG. 10A, powdered silver adjacent to each other are brought into contact, thereby forming an electrode. However, after the stretching, the electrode is partially disconnected (see the right-hand side of FIG. 10A). This is because a mixture amount of the resin binder is limited to ensure the conductivity of the electrode and, thus, it is difficult for the electrode to have enough stretchability, which leads to the partial disconnection of the electrode.
FIG. 10B shows SEM (Scanning Electron Microscope) images of before and after the stretching in the case of forming a wiring on the base film by using an electrode material obtained by mixing powdered silver and a resin binder. FIG. 10B shows that the wiring is partially disconnected after the stretching.